PCT Patent application IL02/00137, published in the English language on 10 Oct. 2002 as WO 02079955 of NDS Ltd., and corresponding U.S. patent application Ser. No. 10/472,286, published on 10 Jul. 2004 as 2004/0111613 of Shen Orr, et al., describes a system and a method for providing variable security mechanisms for securing digital content, in which a single security mechanism is not used for all content. Instead, at least one characteristic or feature of the security mechanism is varied between units, instances or categories of content. Therefore, even if unauthorized access is gained to a single emit of content, the overall integrity and security of the system for content distribution is not compromised. Preferably, security is provided through a general mechanism, which is then varied in order to provide variable, dissimilar security schemes for different types of content. By “type of content”, it is meant any of a single unit of content, a single instance of content or a single category of content. For example, for a category of content, the content may be characterized according to the identity of the content itself, such as the title of a movie for example, and/or according to the owner of a particular copy of the content. Thus, different security schemes may optionally and preferably be generated from a particular root structure.
The Handbook of Applied Cryptography by Alfred J. Menezes, Paul C. van Oorschot, and Scott A. Vanstone, CRC Press, fifth printing (August 2001), is a well known reference for cryptographers, presenting the techniques and algorithms of greatest interest to the current practitioner, along with the supporting motivation and background material. The book is available on the internet at www.cacr.math.uwaterloo.ca/hac.
The disclosures of all references mentioned above and throughout the present specification, as well as the disclosures of all references mentioned in those references, are hereby incorporated herein by reference.